1. Field of the Invention
The present invention generally relates to chromatographic analysis and, in particular, to sample introduction systems, which are adapted for receiving a sample to be analyzed and for delivering the sample to a separation column of a gas chromatograph, and related methods.
2. Description of the Related Art
Gas chromatography is a method for analyzing a sample, which may include one or more analytes, to qualitatively determine the identity of the analytes as well as to quantitatively determine the concentration of each of the analytes. Gas chromatography typically involves a series of steps, including: sample collection, sample preparation, sample introduction into a chromatographic or separation column, chromatographic separation of the sample into individual analytes, detection of those analytes, and data acquisition and reduction.
In order to conduct gas chromatography, a gas chromatograph is utilized which typically incorporates: a sample introduction system configured to receive the sample and to mix the sample with an inert fluid; a separation column through which the various analytes of the sample traverse, and; a detector for measuring the presence of each of the analytes. The design of such a gas chromatograph is based on the premise that the combination of analytes making up the sample will separate as they traverse the separation column at different rates and, subsequently, exit the column at different retention times.
Due to the great variety of separation column configurations and the diversity of samples that can be analyzed, several sample introduction systems are known; however, no single system can best satisfy all analytical requirements. As a general principle, however, a sample introduction system is adapted to provide accurate, reproducible, and predictable introduction of a sample into the separation column of a gas chromatograph. Typically, a sample introduction system includes a sample inlet into which a quantity of sample in liquid form is injected, such as by using a syringe. After injection, the sample then can be prepared, such as by heating, for delivery to the separation column of the gas chromatograph. Additionally, there are other known sample introduction systems that are adapted for introducing samples into a separation column when syringe injection is inappropriate, such as gas or liquid sampling valves, head-space autosamplers, thermal desorbers, purge and trap samplers, and pyrolyzers, for example.
Heretofore, useful techniques for introducing a sample into a chromatographic system have incorporated the use of a heating element for heating the sample, which oftentimes enters the sample introduction system in a liquid phase, so that a gaseous phase of the sample is introduced into the separation column. Typically, sample introduction systems facilitating such a technique have incorporated a sample inlet that is heated with a cartridge heater. Such an inlet heater commonly is formed of a block of material, such as aluminum or stainless steel, for instance, in which the cartridge heater and a temperature sensor is installed and into which the sample introduction column extends. Thus, when heating of the sample is desired, voltage is applied to the cartridge heater installed within the aluminum or stainless steel block, thereby heating the block, with the heat being transferred through the sample introduction column and to the sample predominately by conduction. Although these prior art systems have met with considerable success, they tend to be somewhat inefficient, suffer from slow transient performance, and, oftentimes, require the incorporation of large power supplies.
Therefore, there exists a need for improved systems and methods which address these and other shortcomings of the prior art.
Briefly described, the present invention relates to sample introduction systems, which are adapted for receiving a sample to be analyzed and for delivering the sample to a separation column of a gas chromatograph, and related methods. In a preferred embodiment, a chromatographic analytical instrument system for analyzing a sample incorporates a separation column adapted to receive a mixture of a carrier gas and at least a portion of a sample, and a sample introduction apparatus. Preferably, the sample introduction apparatus includes a wall defining a channel, a coating and a heater controller, with the channel being configured to receive the sample and being adapted to engage in fluid communication with the separation column. The coating preferably is formed at least partially of a semi-conductive material and is arranged adjacent to at least a portion of the wall, and the heater controller electro-magnetically communicates with the coating. So configured, an increase in the temperature of the coating is achieved after the coating receives electro-magnetic energy from the heater controller, thereby allowing the temperature of the sample to increase within the channel.
In accordance with another aspect of the present invention, a preferred embodiment of the sample introduction apparatus includes a wall which defines a channel, with the channel being configured to receive the sample and being adapted to engage in fluid communication with the separation column of the chromatographic apparatus. Preferably, a coating of semi-conductive material is arranged adjacent to at least a portion of the wall. Additionally, a heater controller provides electrical energy to the coating. The electrical energy generates an electric current in the resistive coating and the coating""s electrical resistive properties convert the current flow into heat, that conducts at least a portion of the energy to the sample so that sample temperature increases within the channel of the sample introduction apparatus.
In accordance with another aspect of the present invention, an embodiment of the sample introduction apparatus includes a wall which defines a channel, with the channel being configured to receive the sample and being adapted to engage in fluid communication with the separation column of the chromatographic apparatus. Preferably, a coating of semi-conductive material is arranged adjacent to at least a portion of the wall. Additionally, means for heating the coating is provided. So configured, the coating, in response to the means for heating, conducts heat to the sample so that a temperature of the sample increases within the channel of the sample introduction apparatus.
In accordance with another aspect of the present invention, a method for providing a sample to a chromatographic apparatus comprises the steps of: providing a channel configured to receive the sample, the channel being adapted to engage in fluid communication with the separation column of the chromatographic apparatus, the channel having a coating of semi-conductive material arranged adjacent to at least a portion thereof; heating the coating so that a temperature of the sample increases within the channel, and; providing the sample to the separation column of the chromatographic apparatus.
Other objects, features, and advantages of the present invention will become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such objects, features, and advantages be included herein within the scope of the present invention, as defined in the appended claims.